1. Field of the Invention
Embodiments of the invention generally relate to methods and apparatus for laser reflectometry in substrate processing systems. More specifically, embodiments described herein relate to improving efficiency of laser devices and safety features related to utilization of laser devices in thermal processing systems.
2. Description of the Related Art
Thermal processing is commonly practiced in the semiconductor industry. Semiconductor substrates are subjected to thermal processing in the context of many transformations, including doping, activation, and annealing of gate source, drain, and channel structures, siliciding, crystallization, oxidation, and the like. Over the years, techniques of thermal processing have progressed from simple furnace baking, to various forms of increasingly rapid thermal processing such as RTP, spike annealing, and laser annealing.
Conventional laser annealing processes use laser emitters that may be semiconductor or solid state. A common approach is to image the laser light into a line or thin rectangular image that is scanned across a substrate (or the substrate moved relative to the laser light) to process the entire surface of the substrate.
Metrology techniques are typically utilized to monitor and control the annealing process. In some conventional laser annealing processes, laser reflectometry is utilized to provide real-time metrology information. Laser reflectometry typically utilizes a semiconductor laser (e.g., a diode laser) and a sensor. Light from the semiconductor laser is directed towards the substrate and the light reflected from the substrate is received by the sensor. Information from the sensor is provided to a device for monitoring and/or control of the annealing process.
The use of multiple lasers in an annealing process creates challenges. Light from the laser emitter utilized for annealing may interfere with the light from the semiconductor laser, which may alter the properties of the beam emitted from the semiconductor laser. Likewise, the sensor may be sensitive to light outside of the wavelengths associated with the beam from the semiconductor laser. Thus, light from the laser emitter utilized for annealing may cause deviations in the metrology information. Additionally, the semiconductor laser may require adjustments to the beam to ensure alignment of the beam to a specific target area of the substrate and/or ensure alignment of the beam with the sensor. These adjustments are often performed manually by personnel. However, the intensity of the beam from the semiconductor laser is in a range that is harmful to human vision and/or human skin. Thus, tinted safety glasses and protective clothing are required when the beam is being adjusted. However, the tinted safety glasses may obscure areas of interest and may require personnel to remove the glasses to view the areas of interest. Removal of safety glasses may cause inadvertent exposure to light from the semiconductor laser, which poses a safety risk to personnel.
Thus, there is a need for apparatus and methods for controlling lasers and beams from the lasers in order to enhance metrology information and manage safety risks.